Improved Selectivity in Eliciting Evoked Electromyography Responses With High-Resolution Spinal Cord Stimulation

BACKGROUND AND OBJECTIVES

As spinal cord stimulation (SCS) offers a therapy for increasing numbers of patients with chronic pain and spinal cord injury, it becomes increasingly important to better understand its somatotopy. In this prospective study, we investigate whether high-resolution SCS (HR-SCS) offers improved selectivity assessed through elicitation of evoked electromyography (EMG) responses as compared with commercial paddle leads.

METHODS

Vertical tripole configurations were used to elicit EMG responses in both types of paddles placed for standard-of-care indications between T6 and T10. In HR-SCS, evoked EMG responses in lower extremity/abdominal muscle groups were monitored at 6 to 8 mediolateral sites. All commercial paddle columns were tested. Percentage change in the maximum root mean square value was calculated at a group level. Heat maps were generated to identify responders for each muscle group. Responders were considered patients who had a >50% change in root mean square over baseline.

RESULTS

We demonstrated significantly greater motor responses across medial and lateral contacts and greater responder rates consistently at the T6 and T9 levels with HR-SCS as compared with commercial paddles in 18 patients. Distal muscle groups (gastrocnemius and tibialis anterior) and proximal muscle groups (biceps femoris and quadriceps) were selectively activated at both levels.

CONCLUSION

We demonstrate that HR-SCS has greater selectivity in eliciting evoked EMG responses in an intraoperative setting. HR-SCS offers recruitment of muscle groups at lateral contacts concurrently with medial contacts. We provide data that HR-SCS may provide higher spatial resolution, which has the potential to allow for personalization of care and treatment of pain syndromes/symptoms which to date have not been effectively treated.

The Use of Salvage Procedures for Wound Complications in Neuromodulation

OBJECTIVE

Wound complications are a prevalent concern for neuromodulation procedures. While removal of the device was recommended, attempts to salvage expensive hardware have become commonplace. We examine our management in wound issues to aid in providing guidance for these situations.

METHODS

We identified 40 patients over an 8-year period in a large neuromodulation practice, who underwent washout or partial salvage of hardware. We examined the efficacy of washout and partial explants on the ability to salvage the implants. Covariates including age, sex, body mass index, smoking status, anticoagulation, and device type were considered.

RESULTS

There were 29 washouts and 10 partial hardware removal cases. Washouts were successful in 15/29 cases (51.7%), partial hardware removal was successful in 2/10 cases (20%), and removal with replacement was not successful (0 of 1). Washouts tended to be more successful than partial removal procedures (P = 0.08). In cases of successful washout, the average duration between infectious symptoms and washout was 7.27 ± 2.19 days. None of the demographic variables were associated with increased likelihood of washout failure.

CONCLUSIONS

Our results demonstrate a higher rate of washout failure in those who underwent partial device removal and in the presence of purulence at the surgical site. Further investigation must be conducted to determine the instances in which hardware removal is indicated to prevent failure or removal due to infection. Identification of these parameters will optimize therapeutic benefit and long-term financial impact.

Establishing Minimal Clinically Important Difference in Sleep Outcomes after Spinal Cord Stimulation in Patients with Chronic Pain Disorders

INTRODUCTION

As one of the most common medical conditions for which patients seek medical care, chronic pain can be debilitating. The relationship between chronic pain and sleep is thought to be bidirectional, suggesting that treatment of one can be beneficial to the other. There is mounting evidence that spinal cord stimulation (SCS) improves aspects of sleep. How meaningful that is to patients' lives has not been ascertained.

OBJECTIVE

The aim of the current study was to further elucidate the effect of SCS on sleep by examining the relationship between pain outcome measures with the insomnia severity index (ISI) and to establish the minimally clinical important difference (MCID), which is defined as the smallest noticeable change that an individual perceives as clinically significant.

MATERIALS AND METHODS

We prospectively collected ISI, Epworth sleepiness scale (ESS), Numerical Rating Scale, McGill Pain Questionnaire-Short Form, Oswestry Disability Index, Beck Depression Inventory, and Pain Catastrophizing Scale data both pre- and postoperatively for chronic pain patients who underwent SCS placement and had long-term outcomes. The ISI is a well-studied questionnaire used to assess an individual's level of insomnia.

RESULTS

We correlated the ESS and ISI with pain outcome measures in sixty-four patients at a mean follow-up of 9.8 ± 2.9 months. The ISI showed correlations with disability as measured through the Oswestry Disability Index (p = 0.014) and depression as measured through the Beck Depression Inventory (p = 0.024). MCID values for the ISI were calculated using both anchor- and distribution-based methods. The minimal detectable change method resulted in an MCID of 2.4 points, standard error of measurement resulted in an MCID of 2.6 points, and the change difference resulted in an MCID of 2.45. The receiver operating characteristic method yielded an MCID of 0.5-point change with an area under the curve of 0.61.

CONCLUSION

This study successfully established MCID ranges for the ISI outcome measure to help gauge improvement in insomnia after SCS. The ISI has ample evidence of its validity in assessment of insomnia, and MCID values of 2.4-2.6 correlate with improvement in disability and depression in our patients.

A Pilot Study Comparing Algorithmic Adaptive Conventional Stimulation with High-Dose Stimulation in Chronic Pain Patients

INTRODUCTION

Spinal cord stimulation is an effective method of treatment for chronic pain. We previously showed that programming using accelerometry was advantageous for paresthesia-based stimulation. However, programming can be labor intensive.

OBJECTIVE

Here we focus on standardized programming for both accelerometer-based paresthesia-induced programming (termed "shuffle") and high-dose (HD) subthreshold programming with stimulation delivered over the T9-10 interspace.

METHODS

In this prospective cross-over study, patients received 4 weeks of shuffle programming and 4 weeks of HD programming in a randomized order. In both intervals, contacts overlying T9-10 were programmed. Pain scales with measurements of activity and sleep were collected at the end of each study arm and compared with preoperative baseline scores.

RESULTS

Twelve patients were enrolled, with 10 patients completing this study. Compared with baseline, during the HD study period, significant improvements were seen in worst pain of week (P = 0.03) and current pain (P = 0.04) as rated on Numeric Rating Scale scores and walking on the Activity Test (P = 0.012). No difference was seen from baseline compared with shuffle stimulation or in shuffle stimulation compared with HD stimulation.

CONCLUSION

In this pilot study, we demonstrated that HD stimulation at T9-10 is superior to algorithmic programming of paresthesia-based stimulation. These results compared with our previous work with shuffle suggest that paresthesia-based stimulation may necessitate stimulation of additional contact locations and additional programming to optimize. This algorithmic programming of paresthesia-based stimulation continues to warrant exploration.

Development of Machine Learning-Based Models to Predict Treatment Response to Spinal Cord Stimulation

BACKGROUND

Despite spinal cord stimulation's (SCS) proven efficacy, failure rates are high with no clear understanding of which patients benefit long term. Currently, patient selection for SCS is based on the subjective experience of the implanting physician.

OBJECTIVE

To develop machine learning (ML)-based predictive models of long-term SCS response.

METHODS

A combined unsupervised (clustering) and supervised (classification) ML technique was applied on a prospectively collected cohort of 151 patients, which included 31 features. Clusters identified using unsupervised K-means clustering were fitted with individualized predictive models of logistic regression, random forest, and XGBoost.

RESULTS

Two distinct clusters were found, and patients in the cohorts significantly differed in age, duration of chronic pain, preoperative numeric rating scale, and preoperative pain catastrophizing scale scores. Using the 10 most influential features, logistic regression predictive models with a nested cross-validation demonstrated the highest overall performance with the area under the curve of 0.757 and 0.708 for each respective cluster.

CONCLUSION

This combined unsupervised-supervised learning approach yielded high predictive performance, suggesting that advanced ML-derived approaches have potential to be used as a functional clinical tool to improve long-term SCS outcomes. Further studies are needed for optimization and external validation of these models.

Benefit of Intracystic Bleomycin for Symptomatic Recurrent Rathke Cleft Cyst

BACKGROUND

Management of recurrent Rathke cleft cysts (RCC) is problematic. The mainstay of treatment has been reoperation with cyst drainage. Radical cyst resection, although effective, results in a high incidence of diabetes insipidus. Several case reports suggest a potential benefit to radiation therapy or the use of intracystic bleomycin. The intracystic application of bleomycin is known to be beneficial in the treatment of cystic craniopharyngioma; however, its usefulness in the treatment of recurrent RCC has yet to be proven.

OBJECTIVE

To present our 6-yr experience using intracystic bleomycin for recurrent RCC.

METHODS

We performed a retrospective chart review of patients with RCC who underwent surgical resection between January 2010 and May 2016 by a single surgeon. Specific attention was paid to patients with recurrent RCC.

RESULTS

Of the 59 patients operated on for RCC during this 6-yr interval, 6 patients with symptomatic recurrent RCC were identified and received intracystic bleomycin at the time of reoperation. To date, no symptomatic cyst recurrence has been documented in the patients receiving bleomycin (mean = 38.8 mo, range 21.2-79.8 mo).

CONCLUSION

The use of intracystic bleomycin appears to be a safe and potentially effective treatment option in patients with recurrent RCC. Additional studies with longer follow-up are needed to further define the role of bleomycin in recurrent RCC.

Golgi Analysis of Neuron Morphology in the Presumptive Somatosensory Cortex and Visual Cortex of the Florida Manatee (Trichechus manatus latirostris)

The current study investigates neuron morphology in presumptive primary somatosensory (S1) and primary visual (V1) cortices of the Florida manatee (Trichechus manatus latirostris) as revealed by Golgi impregnation. Sirenians, including manatees, have an aquatic lifestyle, a large body size, and a relatively large lissencephalic brain. The present study examines neuron morphology in 3 cortical areas: in S1, dorsolateral cortex area 1 (DL1) and cluster cortex area 2 (CL2) and in V1, dorsolateral cortex area 4 (DL4). Neurons exhibited a variety of morphological types, with pyramidal neurons being the most common. The large variety of neuron types present in the manatee cortex was comparable to that seen in other eutherian mammals, except for rodents and primates, where pyramid-shaped neurons predominate. A comparison between pyramidal neurons in S1 and V1 indicated relatively greater dendritic branching in S1. Across all 3 areas, the dendritic arborization pattern of pyramidal neurons was also similar to that observed previously in the afrotherian rock hyrax, cetartiodactyls, opossums, and echidnas but did not resemble the widely bifurcated dendrites seen in the large-brained African elephant. Despite adaptations for an aquatic environment, manatees did not share specific neuron types such as tritufted and star-like neurons that have been found in cetaceans. Manatees exhibit an evolutionarily primitive pattern of cortical neuron morphology shared with most other mammals and do not appear to have neuronal specializations for an aquatic niche.

The influence of context on students' approaches to learning: a case study

This paper gives an account of a small-scale longitudinal study that examined changes in conceptions and approaches to learning as 14 students experience a problem-based learning (PBL) curriculum for the first time. The course in oral biology aimed to encourage conceptual understanding of the topic and improve student learning through its PBL curriculum and assessment method. Those who entered the course with a surface approach and fragmented conception of learning left with a deep-learning approach, cohesive conception and quality learning outcomes. There were no observable changes in the students who started the course with a deep-learning approach and cohesive conception, except for two who reported surface approaches and fragmented conceptions at the end. These two students also achieved the lowest examination scores. To help explain these findings we examine the wider context for student learning including student motivation.